This application claims the priority of Korean Patent Application No. 2002-67053, filed on Oct. 31, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a high frequency optical oscillator in the field of wireless telecommunications, and more particularly, to a millimeter wave band frequency optical oscillator.
2. Description of the Related Art
Next-generation ultra-speed wireless Internet services can transmit a large capacity (about 100 Mbps) of information, which is 10 times or greater than the information transmitted by existing wireless Internet service, to wireless subscribers. In order to achieve this, millimeter wave wireless transmission systems that transmit a large capacity of information have been actively developed. In the millimeter wave wireless transmission systems, a millimeter wave band frequency optical oscillator is anticipated to be used as a millimeter wave oscillating frequency signal source in a base station and also as an optical line network between base stations.
In the field of millimeter wave wireless transmission systems, optical oscillators using semiconductor high frequency optical modulators and optical oscillators using a resonator modulation method have been developed up to now. The optical oscillators using optical modulators have a frequency band limited to 30 GHz at most, and accordingly they are not suitable for a frequency band that is being currently studied. Also, the optical oscillators using optical modulators are not practical because it is difficult to manufacture an optical source. On the other hand, the present applicant has continuously reported improved versions of the optical oscillators using a resonator modulation.
For example, the present applicant has Korean Patent Application No. 1999-61149 filed on Dec. 23, 1999, which discloses an optical oscillator capable of being modulated to a maximum of 20 GHz due to a beat phenomenon occurring between two laser modes by oscillating the two laser modes within a resonator formed by combining a fiber-ring laser resonator and a fiber linear laser resonator using a 50% fiber coupler. The present applicant also has Korean Patent Application No. 2000-54801 filed on Sep. 19, 2000, which discloses an oscillator capable of being modulated to a maximum frequency of 40 GHz at most by combining two fiber-ring laser resonators using the 50% fiber coupler.
The optical oscillators proposed by the present applicants are improved versions of conventional optical oscillators but have complicated structures because two individual fiber laser resonators must be combined using a fiber coupler. In addition, in order to be used as a millimeter wave oscillating frequency signal source, the proposed optical oscillators require to be modulated to a wider frequency band.